The role of the Agulhas in the Benguela Current System: A numerical modelling approach

A modelling approach is used to investigate the influence of the Agulhas on the southern Benguela system. Two climatological ROMS simulations are run that are identical except that in one of them the effect of the Agulhas is removed. Comparing their output allows for a clear indication of the role of the Agulhas on both the large-scale and shelf dynamics. About 15 Sv of the mean transport of the Benguela Current is shown to be contributed by Agulhas influx, with the most intense flow being associated with extreme turbulence and its meandering nature is a reflection of the passage of Agulhas Rings. The injection of warm water is particularly evident beyond the shelf-edge, producing a perennially intense cross-shelf density front that is enhanced during upwelling season. This gradient drives a jet that is fastest at the shelf-edge but that extends from the mid-shelf to at least 100 km beyond it and is associated with dynamic uplift via vortex squashing. Similarly generated is the Good Hope Jet that extends northwestward from the western Agulhas Bank. Turbulence associated with Agulhas leakage increases rapidly beyond the shelf-edge causing the upwelling front in the southern Benguela to be subject to intense mixing, leaving a relatively uniform front there. Locally generated regions of high turbulence exist in the vicinity of the shelf-edge jets as well as further north in association with the large filaments that originate from the perennial Lüderitz upwelling cell, with or without the influence of the Agulha